N.Y.C. Admin. Code § BC 1605: Section BC 1605: Load Combinations

1605.1 General.

Buildings and other structures and portions thereof shall be designed to resist:

1. The load combinations specified in Section 1605.2 or 1605.3;

2. The load combinations specified in Chapters 18 through 23; and

3. The seismic load effects including overstrength factor in accordance with Sections 2.3.6 and 2.4.5 of ASCE 7 where required by Chapters 12, 13, and 15 of ASCE 7. With the simplified procedure of Section 12.14 of ASCE 7, the seismic load effects including overstrength factor in accordance with Section 12.14.3.2 and Chapter 2 of ASCE 7 shall be used.

Applicable loads shall be considered, including both earthquake and wind, in accordance with the specified load combinations. Each load combination shall also be investigated with one or more of the variable loads set to zero.

Where the load combinations with overstrength factor in Sections 2.3.6 and 2.4.5 of ASCE 7 apply, they shall be used as follows

1. The basic combinations for strength design with overstrength factor in lieu of Equations 16-5 and 16-7 in Section 1605.2.

2. The basic combinations for allowable stress design with overstrength factor in lieu of Equations 16-12, 16-14 and 16-16 in Section 1605.3.1.

1605.1.1 Stability.

Regardless of which load combinations are used to design for strength, where overall structure stability (such as stability against overturning, sliding, or buoyancy) is being verified, use of the load combinations specified in Section 1605.2 or 1605.3 shall be permitted. Where the load combinations specified in Section 1605.2 are used, strength reduction factors applicable to soil resistance shall be provided by a registered design professional. The stability of retaining walls shall be verified in accordance with Section 1807.2.

1605.2 Load combinations using strength design or load and resistance factor design.

Where strength design or load and resistance factor design is used, buildings and other structures, and portions thereof, shall be designed to resist the most critical effects resulting from the following combinations of factored loads:

1.4 (D + F)

(Equation 16-1) 

1.2 (D + F) + 1.6 (L + H) + 0.5 (L

r

or S or R)

(Equation 16-2) 

1.2 (D + F) + 1.6 (L

r

or S or R) + 1.6H + (f

1

L or 0.5W)

(Equation 16-3) 

1.2 (D + F) + 1.0W + f

1

L + 1.6H + 0.5 (L

r

or S or R)

(Equation 16-4) 

1.2 (D + F) + 1.0E + f

1

L + 1.6H +f

2

S

(Equation 16-5) 

0.9D + 1.0W + 1.6H

(Equation 16-6) 

0.9 (D + F) + 1.0E + 1.6H

(Equation 16-7)

where:

f

1

= 1 for places of public assembly live loads in excess of 100 pounds per square foot (4.79 kN/m

2

), and parking garages; and 0.5 for other live loads.

f

2

= 0.7 for roof configurations (such as saw tooth) that do not shed snow off the structure, and 0.2 for other roof configurations.

Exceptions:

1. Where other factored load combinations are specifically required by other provisions of this code, such combinations shall take precedence.

2. Where the effect of H resists the primary variable load effect, a load factor of 0.9 shall be included with H where H is permanent and H shall be set to zero for all other conditions.

1605.2.1 Other loads.

Where a structure is located in a V zone or Coastal A zone and F

a

is to be considered in design, in addition to the load combinations of Equations 16-1 through 16-7, the structure and portions thereof shall resist the most critical effects of the load combinations of Equations 16-8 and 16-10. Where a structure is located in an A zone and F

a

is to be considered in design, in addition to the load combinations of Equations 16-1 through 16-7, structures and portions thereof shall resist the most critical effects of the load combinations of Equation 16-9 and 16-11. Where self-straining loads, T, are considered in design, their structural effects in combination with other loads shall be determined in accordance with Section 2.3.4 of ASCE 7. Where ice loads are to be considered in design, the load combinations of Section 2.3.3 of ASCE 7 shall be used. Refer to the following sections for other load combinations:

Flood Load Combinations:

1.2 (D + F) + 1.0W + 2.0F

a

+ f

1

L + 1.6H + 0.5 (L

r

or S or R)

(Equation 16-8) 

1.2 (D + F) + 0.5W + 1.0F

a

+ f

1

L + 1.6H + 0.5 (L

r

or S or R)

(Equation 16-9) 

0.9D + 1.0W + 2.0F

a

+ 1.6H

(Equation 16-10) 

0.9D + 0.5W + 1.0F

a

+ 1.6H

(Equation 16-11)

1605.3 Load combinations using allowable stress design.

Load combinations for allowable stress design shall be in accordance with Section 1605.3.1 or 1605.4.

1605.3.1 Basic load combinations.

Where allowable stress design (working stress design), as permitted by this code, is used, structures and portions thereof shall resist the most critical effects resulting from the following combinations of loads:

D + F

(Equation 16-12) 

 D + H + F + L

(Equation 16-13) 

 D + H + F + (L

r

or S or R)

(Equation 16-14) 

 D + H + F + 0.75 (L) + 0.75 (L

r

or S or R)

(Equation 16-15) 

 D + H + F + (0.6W or 0.7E)

(Equation 16-16) 

D + H + F + 0.75 (W or 0.7E) + 0.75L + 0.75 (L

r

or S or R)

(Equation 16-17) 

D + H + F + 0.75 (0.7E) + 0.75L + 0.75S

(Equation 16-18) 

0.6D + 0.6W + H

(Equation 16-19) 

0.6 (D + F) + 0.7E + H

(Equation 16-20)

Exceptions:

1. Crane hook loads need not be combined with roof live load or with more than three-fourths of the snow load or one-half of the wind load.

2. Flat roof snow loads of 30 psf (1.44 kN/m

2

) or less and roof live loads of 30 psf (1.44 kN/m

2

) or less need not be combined with seismic loads. Where flat roof snow loads exceed 30 psf (1.44 kN/m

2

), 20 percent shall be combined with seismic loads.

3. Where the effect of H resists the primary variable load effect, a load factor of 0.6 shall be included with H where H is permanent and H shall be set to zero for all other conditions.

4. In Equation 16-19, the wind load, W, is permitted to be reduced in accordance with Exception 2 of Section 2.4.1 of ASCE 7.

5. In Equation 16-20, 0.6D is permitted to be increased to 0.9D for the design of special reinforced masonry shear walls complying with Chapter 21.

1605.3.1.1 Stress increases.

Increases in allowable stresses specified in the appropriate material chapter or the referenced standards shall not be used with the load combinations of Section 1605.3.1, except that increases shall be permitted in accordance with Chapter 23.

1605.3.1.2 Other loads.

Where a structure is located in a V zone or Coastal A zone and F

a

is to be considered in design, in addition to load combinations of Equations 16-12 through 16-20, structures and portions thereof shall resist the most critical effects of load combinations of Equations 16-21, 16-23 and 16-25. Where a structure is located in an A zone and F

a

is to be considered in design, in addition to load combinations of Equations 16-12 through 16-20, structures and portions thereof shall resist the most critical effects of load combinations of Equations 16-22, 16-24 and 16-26. Where self-straining loads, T, are considered in design, their structural effects in combination with other loads shall be determined in accordance with Section 2.4.4 of ASCE 7. Where ice loads are to be considered in design, the load combinations of Section 2.4.3 of ASCE 7 shall be used.

Flood Load Combinations:

D + H + F + 0.6W + 1.5F

a

(Equation 16-21)

D + H + F + 0.6W + 0.75F

a

(Equation 16-22)

D + H + F + 0.75 (0.6W) + 0.75L + 0.75 (L

r

or S or R) + 1.5F

a

(Equation 16-23) 

D + H + F + 0.75 (0.6W) + 0.75L + 0.75 (L

r

or S or R) + 0.75F

a

(Equation 16-24) 

0.6D + 0.6W + H + 1.5F

a

(Equation 16-25) 

0.6D + 0.6W + H + 0.75F

a

(Equation 16-26)

1605.4 Structural integrity load combinations – alternate load path method.

Where specifically required by Sections 1615 through 1617, elements and components shall be designed to resist the forces calculated using the following combination of factored loads:

D + f

1

L + f

2

W

(Equation 16-27)

Where:

f

1

= 0.25 for buildings in Risk Category II.

f

1

= 0.5 for buildings in Risk Category III or IV.

f

2

= 0 for buildings in Risk Category II.

f

2

= 0.33 for buildings in Risk Category III or IV.

The live load component f

1

L need not be greater than the reduced live load.

1605.5 Structural integrity load combinations – vehicular impact and gas explosions.

Where specifically required by Sections 1616.4 and 1616.5, elements and components shall be designed to resist the forces calculated using the following combination of factored loads:

1.2D + A

k

(0.5L or 0.2S)

(Equation 16-28) 

0.9D + A

k

+ 0.2W

(Equation 16-29)

where:

A

k

is the load effect of the vehicular impact or gas explosion.

1605.6 Structural integrity load combinations – specific local resistance method.

Where the specific local resistance method is used in a key element analysis, the specified local loads shall be used as specified in Section 1617.6.